Optical path difference compensation mechanism for acquiring wave form signal of time-domain pulsed spectrometer

ABSTRACT

It is an object to provide a time-domain pulsed spectroscopy apparatus in which time-domain pulsed spectroscopy of multiple samples, states thereof, and so on can be carried out easily and in a short period of time. A time-domain pulsed spectroscopy apparatus of the present invention comprises a pulsed laser light source; a splitting unit configured to split pulsed laser light from the pulsed laser light source into excitation pulsed laser light and detection pulsed laser light; a pulsed-light emitting unit; a detector; a sample holder configured to hold the sample; and sample-unit entrance and exit optical systems configured to guide the pulsed light from the pulsed-light emitting unit to the sample and to guide to the detector pulsed light reflected from or transmitted through the sample due to the irradiation; wherein the time-domain pulsed spectroscopy apparatus further comprises: at least one optical-path-length varying unit for setting a photometric range, disposed in an incident-side optical path from the splitting unit to the pulsed-light emitting unit and/or in a detection-side optical path from the splitting unit to the detector; and at least one optical delay unit for the wave form signal measurement, disposed in the incident-side optical path from the splitting unit to the pulsed-light emitting unit and/or in the detection-side optical path from the splitting unit to the detector.

TECHNICAL FIELD

The present invention relates to a time-domain pulsed spectroscopyapparatus, and in particular, to a scanning mechanism and optical systemalignment structure (optical arrangement) for acquiring a wave formsignal thereof.

BACKGROUND ART

Due to the practical adoption of ultrashort pulsed laser technology inrecent years, emission techniques and detection techniques for pulsed,coherent, far-infrared (particularly in the terahertz region)electromagnetic waves have progressed rapidly. Accordingly, time-domainpulsed spectroscopy using these pulsed far-infrared electromagneticwaves has become possible, and the pioneering development of practicaltime-domain pulsed spectroscopy apparatuses has progressed in Japan too.

Time-domain pulsed spectroscopy is a spectroscopy method in which, bymeasuring the time-dependent electric field intensity of the pulsedelectromagnetic field and by Fourier transforming this time-dependentdata (time-series data), the electric field intensity and phase ofindividual frequency components forming this pulse are obtained. Onefeature of this spectroscopy method is that the measurement wavelengthrange is the boundary region between light and electromagnetic waves,which is difficult to achieve with conventional measurement. Therefore,this spectroscopy method is expected to elucidate the properties ofnovel materials and new phenomena. Furthermore, only the electric fieldintensity of an electromagnetic wave can be obtained with conventionalspectroscopy methods; however, this time-domain pulsed spectroscopymethod has the unique feature that, by directly measuring temporalchanges in the electric field intensity of electromagnetic waves, it canobtain not only the electric field intensity (amplitude) of theelectromagnetic waves, but also the phase thereof. Therefore, it ispossible to obtain a phase-shift spectrum by comparison with a casewhere there is no sample. Because the phase shift is proportional to thewave vector, it is possible to determine the dispersion relation in thesample using this spectroscopy method, and it is also possible todetermine the dielectric constant of a dielectric from this dispersionrelation (see Japanese Unexamined Patent Application Publication No.2002-277394).

FIG. 1 shows one example of a conventional time-domain pulsedspectroscopy apparatus.

Reference numeral 1 is a light source for emitting femtosecond laser.Femtosecond laser light L1 emitted from the light source 1 is split at abeam splitter (splitting unit) 2. One of the femtosecond lasers isradiated onto a pulsed-light emitting unit 5 as excitation pulsed laserlight (pump pulsed light) L2. At this time, after being modulated by anoptical chopper 3, the excitation pulsed laser light L2 is focused by anobjective lens 4. This pulsed-light emitting unit 5 is, for example, aphotoconductive element in which an electric current flows momentarilywhen the excitation pulsed laser light L2 is radiated, and emits afar-infrared electromagnetic pulse. This far-infrared electromagneticpulse is guided by parabolic mirrors and is irradiated onto ameasurement sample 8. Reflected or transmitted pulsed electromagneticwaves (in this example, transmitted pulsed electromagnetic waves) fromthe sample 8 are guided to a detector 12 by parabolic mirrors 9 and 10.

The other laser light split at the beam splitter 2 is guided to thedetector 12 as detection pulsed laser light (sampling pulsed light) L3.This detector 12, which is also, for example, a photoconductive element,becomes conductive only for the instant when the detection pulsed laserlight L3 is irradiated; therefore, it is possible to detect the electricfield intensity of the reflected or transmitted pulsed electromagneticwaves from the sample 8, arriving at that instant, as an electricalcurrent. A wave form signal of the electric field intensity of thereflected or transmitted pulsed electromagnetic waves from the sample 8can be obtained by applying a delay time at predetermined time intervalsto the detection pulsed laser light L3 with respect to the excitationpulsed laser light L2 using an optical delay unit 13 (or 14). In thisexample, in addition to the optical delay unit 13 (or 14) for wave formsignal measurement, an optical delay unit 14 (or 13) for adjusting thetemporal origin is also provided.

Each item of time-resolved data of the electric field intensity of thereflected or transmitted electromagnetic waves from the sample 8 isprocessed by a signal processing unit. More specifically, the data istransferred to a computer 17 via a lock-in amplifier 16 and is thenstored as time-series data, and amplitude and phase spectra of theelectric field intensity of the reflected or transmitted electromagneticwaves from the sample 8 are obtained by applying Fourier transformprocessing to one sequence of time-series data in the computer 17 totransform it into vibration-frequency (frequency) space.

[Patent Document 1] Japanese Unexamined Patent Application PublicationNo. 2003-131137.

[Patent Document 2] Japanese Unexamined Patent Application PublicationNo. 2003-121355.

[Patent Document 3] Japanese Unexamined Patent Application PublicationNo. 2003-83888.

[Patent Document 4] Japanese Unexamined Patent Application PublicationNo. 2003-75251.

[Patent Document 5] Japanese Unexamined Patent Application PublicationNo. 2003-14620.

[Patent Document 6] Japanese Unexamined Patent Application PublicationNo. 2002-277393.

[Patent Document 7] Japanese Unexamined Patent Application PublicationNo. 2002-277394.

[Patent Document 8] Japanese Unexamined Patent Application PublicationNo. 2002-257629.

[Patent Document 9] Japanese Unexamined Patent Application PublicationNo. 2002-243416.

[Patent Document 10] Japanese Unexamined Patent Application PublicationNo. 2002-98634.

[Patent Document 11] Japanese Unexamined Patent Application PublicationNo. 2001-141567.

[Patent Document 12] Japanese Unexamined Patent Application PublicationNo. 2001-66375.

[Patent Document 13] Japanese Unexamined Patent Application PublicationNo. 2001-21503.

[Patent Document 14] Japanese Unexamined Patent Application PublicationNo. 2001-275103.

[Non-patent Document 1] Q. Wu and X.-C. Zhang, Appl. Phys. Lctt. 67(1995) 3523).

[Non-patent Document 2] M. Tani, S. Matsuura, K. Sakai, and S.Nakashima, Appl. Opt. 36 (1997) 7853.

[Non-patent Document 3] Kiyomi SAKAI, Bunko Kenkyu (Spectroscopy), 50(2001) 261. [Non-patent Document 4] Seiji KOJIMA, Seiji NISHIZAWA, andMitsuo TAKEDA, Bunko Kenkyu (Spectroscopy), 52 (2003) 69.

DISCLOSURE OF INVENTION

The above time-domain pulsed spectroscopy apparatus is not limited toincluding the far-infrared wavelength region in the spectroscopicmeasurement range, which is difficult using a conventional spectroscopyapparatus, and can independently measure not only the intensitydistribution but also the phase distribution in the measurement spectrathereof. Furthermore, time-resolved spectroscopy for observing apicosecond-domain transient phenomenon in real-time is also possible.Due to the provision of such features, the type, state (solid, liquid,gas, etc.) and so on of samples that can be measured or that are desiredto be measured with the time-domain pulsed spectroscopy apparatus covera wide range. However, in order to carry out time-domain spectroscopy ofsuch a wide range of samples and states thereof, different opticalsystems or optical arrangements are required accordingly, and therefore,there is a drawback in that a substantial burden is placed on theoperator and, in addition, a long time is required for preparation andso on until measurement starts, after replacing the sample.

Therefore, the present invention has been conceived in light of thecircumstances described above, and it is an object thereof to provide atime-domain pulsed spectroscopy apparatus that can perform time-domainpulsed spectroscopy of a variety of samples and states thereof, easilyand in a short period of time.

In order to achieve the object described above, the present inventionemploys the following configurations.

A time-domain pulsed spectroscopy apparatus of the present inventioncomprises a pulsed laser light source; a splitting unit configured tosplit pulsed laser light from the pulsed laser light source intoexcitation pulsed laser light and detection pulsed laser light; apulsed-light emitting unit configured to emit pulsed light includingwavelengths in the far-infrared wavelength region due to irradiation ofthe excitation pulsed laser; a detector configured to detect a wave formsignal of the electric field intensity of reflected or transmittedpulsed light from the sample onto which the pulsed light from thepulsed-light emitting unit is radiated; a sample holder configured tohold the sample; and sample-unit entrance and exit optical systemsconfigured to guide the pulsed light from the pulsed-light emitting unitto the sample and to guide to the detector pulsed light reflected fromor transmitted through the sample due to the irradiation; wherein thetime-domain pulsed spectroscopy apparatus further comprises at least oneoptical-path-length varying unit for setting a photometric range,disposed in an incident-side optical path from the splitting unit to thepulsed-light emitting unit and/or in a detection-side optical path fromthe splitting unit to the detector; and at least one optical delay unitfor the wave form signal measurement, disposed in the incident-sideoptical path from the splitting unit to the pulsed-light emitting unitand/or in the detection-side optical path from the splitting unit to thedetector.

Here, “sample-unit entrance and exit optical systems” are opticalsystems including optical systems before and after a sample for whichreplacement and adjustment of the optical systems and/or changing andadjustment of the optical arrangement is necessary when changing thetype or state of the sample, and means optical systems disposed betweenthe pulsed-light emitting unit and the detector.

“Optical-path-length varying unit for setting a photometric range” is adevice for compensating for changes in the optical path length when theoptical path lengths of the sample-unit entrance and exit opticalsystems change due to replacement of the optical systems and/orvariations in the optical arrangement as a result of changing, forexample, the type or state of the sample, and for setting themeasurement start position of the wave form signal of the electric fieldintensity of a pulsed electromagnetic wave reflected from or transmittedthrough the sample. In particular, it means a device having aconfiguration that can compensate for large changes in the optical pathlength, for example, simply by scanning a reflector, even for largechanges in the optical path length as a result of replacing the opticalsystem.

The variation in optical path length by the optical-path-length varyingunit may be achieved by a configuration that can vary sequentially it ora configuration that can vary it non-sequentially. In other words, itmay be a configuration that sequentially varies the optical path lengthby, for example, scanning a reflector disposed in the optical path, oralternatively, it may be a configuration in which an optical path forwhich the photometric range is set for one sample is switched by meansof a reflecting mirror and changed to an optical path that sets thephotometric range for another sample.

“Optical delay unit for wave form signal measurement” is a device inwhich each optical delay unit has the same functionality as theconventional optical delay unit for wave form signal measurement(reference numerals 13 and 14 in FIG. 1); however, when multiple opticaldelay units are provided, it differs from the conventional optical delayunit in that it has a configuration capable of measuring a wave formsignal over a period of time that is increased according to the numberof optical delay units.

It goes without saying that various arrangements are possible for the“optical-length varying unit for setting a photometric range” and the“optical delay unit for wave form signal measurement”, regardless ofwhether they are parallel arrangements or series arrangements.

According to the present invention, when the optical path length of thesample-unit entrance and exit optical systems changes, an advantage isprovided in that it is possible to compensate for that change in opticalpath length and to set the measurement starting position of a wave formsignal of the electric field intensity of a reflected or transmittedpulsed electromagnetic wave from the sample. In particular, even for alarge change in optical path length as a result of replacing the opticalsystem, an advantage is afforded in that it is possible to compensatefor that large change in optical path length using theoptical-path-length varying unit for setting the measurement range. Afurther advantage is provided in that the photometric range can befreely set. When a plurality of optical delay units for wave form signalmeasurement are provided, an advantage is provided in that measurementof the wave form signal is possible over a time period that is increasedby an amount according to the number of optical delay units.

Furthermore, in the time-domain pulsed spectroscopy apparatus of thepresent invention, the optical-path-length varying unit for setting aphotometric range is a movable reflector.

The “movable reflector for setting the photometric range” is a reflectorof the type that can vary the optical path length typically by scanning,but it may be based on a technology that is completely different fromthe conventional reflector (reference numeral 13 or 14 in FIG. 1) foradjusting the temporal origin, required as a result of adjusting theoptical arrangement. In other words, regarding the actual difference inconfiguration, because the conventional reflector for adjusting thetemporal origin adjusts the temporal origin which is shifted in opticaladjustment carried out during measurement, and it does not matter if thescanning range of the reflector is reduced, it is sufficient to providea single reflector. With the apparatus, by also providing the functionfor adjusting the temporal origin in the “optical delay unit for waveform signal measurement”, there are some cases where a reflector foradjusting the temporal origin need not be independently provided, whichmeans that the reflector for adjusting the temporal origin is not anessential component. Accordingly, the movable reflector for setting thephotometric range in the present invention is an essential component ofthe present invention and enables even large variations in the opticalpath length to be compensated for; therefore, a noticeably widerscanning range combining one, two, or more movable reflectors forsetting the photometric range is formed compared with the reflector foradjusting the temporal origin. Therefore, providing a larger number ofreflectors results in a configuration that is capable of widening thescanning region even more. Accordingly, the movable reflector forsetting the photometric range in the present invention features anoperating method that is completely different from the conventional onefor a scannable reflector, and can thus be considered advantageous inthat it enables simple measurement merely by scanning the reflector forsetting the photometric range, even for a wide range of samples forwhich a large change in optical path length is unavoidable.

Furthermore, the “movable reflector for setting the photometric range”is a structure in which, by disposing a plurality of reflectors inparallel when the scanning distance of one reflector cannot be increasedabove an upper size limit, it is possible to ensure a longer opticalpath length by an amount corresponding to the number of thesereflectors.

It goes without saying that the “movable reflector for setting thephotometric range” is not limited to setting the measurement startposition of the wave form signal but can also be used for adjusting thetemporal origin, and it can be used to set various photometric rangeswhich require changes in the optical path length.

The “movable reflector for setting the measurement range” is areflecting mirror such as a corner cube mirror, for example, but it isnot limited thereto.

According to the present invention, an advantage is provided in that itis possible to continuously vary the optical path length.

In the time-domain pulsed spectroscopy apparatus of the presentinvention, the optical-path-length varying unit for setting ameasurement range is a movable or fixed reflector; and either reflectorincludes, at the incident side of the pulsed light to the reflector, agate member configured to pass or block the pulsed light to thereflector, and by switching between passing or blocking, it is possibleto add an optical path via one, two, or more of the reflectors to extendthe optical path length and/or to skip one, two, or more of thereflectors to shorten the optical path length.

The gate member is, for example, a reflecting mirror and switches theoptical path of the pulsed light by inserting and removing thisreflecting mirror into and from the optical path to vary the opticalpath length. In other words, by inserting and removing the reflectingmirror, the pulsed light is incident on a predetermined reflector orblocked, and the optical path via that reflector can be added to extendthe optical path length, or that reflector can be skipped to reduce theoptical path length.

The gate member may be configured to pass and block the pulsed lightwithout moving it spatially.

The switching between passing and blocking states of the gate member maybe automatic or manual, and variation of the optical path length may becarried out by a plurality of gate members.

According to the present invention, an advantage is provided in that itis possible to vary the optical path length without moving the reflectorspatially. In other words, an advantage is provided in that, since theoptical path length can be varied even with a fixed reflector, it ispossible to construct a low-cost apparatus. An advantage is alsoprovided in that it is possible to select a reflector to be used fromamong a plurality of reflectors, and it is possible to freely set theoptical path according to the measurement. Therefore, an advantage isafforded in that it is possible to select a reflector to be used and toperform measurement for each measurement of the same sample, not justeach time the sample is replaced. Furthermore, when a problem occurswith one, two, or more reflectors of the plurality of reflectors, anadvantage is afforded in that it is also possible to replace thatreflector and set the optical path. Moreover, an advantage is affordedin that a wider range of arrangements is possible in terms of theoptical arrangement of the optical system involving a plurality ofreflectors.

Furthermore, in the time-domain pulsed spectroscopy apparatus of thepresent invention, passing or blocking of at least one of the gatemembers is performed by inserting and removing the gate member, bytranslational motion, into and from the optical path.

The gate member may be configured to be translated together with thereflector.

Furthermore, in the time-domain pulsed spectroscopy apparatus of thepresent invention, passing or blocking of at least one of the gatemembers is performed by inserting and removing the gate member, byrotation, into and from the optical path.

Here, the term “rotation” includes all cases where the optical pathswitching operation can be accomplished by rotationally driving the gatemember.

Furthermore, the time-domain pulsed spectroscopy apparatus of thepresent invention further includes a driving device configured toautomatically scan the optical-path-length varying unit and/or theoptical delay unit; and a computer control apparatus configured toautomatically control the driving device.

Here, as the “driving device”, it is possible to use a standard drivingdevice for scanning, such as a stepping motor, for example.

According to the present invention, an advantage is provided in that itis possible to automatically scan the optical-path-length varying unitand/or the optical delay unit, and the scanning thereof can beautomatically controlled by the computer.

Furthermore, in the time-domain pulsed spectroscopy apparatus of thepresent invention, the sample holder and the sample-unit entrance andexit optical systems are provided inside an auxiliary optical unit thatcan be attached to enable replacement thereof.

The auxiliary optical unit is preferably a specialized unit providedwith sample-unit entrance and exit optical systems with optimum designsfor each sample.

With this time-domain pulsed spectroscopy apparatus, the spatialdimensions of the apparatus equipped with the auxiliary optical unit canbe set within a range that allows changes in the optical path length tobe corrected by the scannable reflector for setting the photometricrange. Therefore, the spatial dimensions are, for example, a width of150 mm or more, a depth of 180 mm or more, and a height of 150 mm ormore.

According to the present invention, because a large change in theoptical path length as a result of replacing the auxiliary optical unitcan be compensated using the optical-path-length varying unit forsetting the photometric range, an advantage is provided in that thepreparation time until commencement of measurement can be reduced. Also,by using a specialized auxiliary optical unit provided with sample-unitentrance and exit optical systems having optimum designs for eachsample, an advantage is afforded in that it is not necessary to adjustthe sample-unit entrance and exit optical systems when replacing theauxiliary optical unit.

Furthermore, the time-domain pulsed spectroscopy of the presentinvention has an optical design such that provides optical alignmentwith respect to the auxiliary optical unit.

Here, the term “provides optical alignment” means that the FOV (Field ofview) values match.

According to the present invention, an advantage is afforded in that itis possible to prevent light loss at the connection portion between theauxiliary optical unit and the apparatus, even as a result of replacingthe auxiliary optical unit.

Furthermore, in a time-domain pulsed spectroscopy apparatus comprising apulsed laser light source; a splitting unit configured to split pulsedlaser light from the pulsed laser light source into excitation pulsedlaser light and detection pulsed laser light; a pulsed-light emittingunit configured to emit pulsed light including wavelengths in thefar-infrared wavelength region due to irradiation of the excitationpulsed laser; a detector configured to detect a wave form signal of theelectric field intensity of reflected or transmitted pulsed light fromthe sample onto which the pulsed light from the pulsed-light emittingunit is radiated; a sample holder configured to hold the sample; andsample-unit entrance and exit optical systems configured to guide thepulsed light from the pulsed-light emitting unit to the sample and toguide pulsed light reflected from or transmitted through the sample dueto the irradiation towards the detector; the present invention ischaracterized in that, from the pulsed-light emitting unit to thesample-unit entrance and exit optical systems and/or from the detectorto the sample-unit entrance and exit optical systems, one or a pluralityof planar mirrors and one or a plurality of aspherical mirrors aredisposed in this order.

The aspherical mirror disposed in the incident-side optical path betweenthe pulsed-light emitting unit and the sample-unit entrance and exitoptical systems converges the pulsed light towards the sample. On theother hand, the planar mirror is disposed between the pulsed-lightemitting unit and the aspherical mirror and deflects the pulsed lightemitted from the pulsed-light emitting unit. Therefore, the optical pathlength of the pulsed-light emitting unit and the aspherical mirror canbe increased. By increasing this optical path length, it is possible toreduce, as much as possible, the focal area focused by the asphericalmirror, and consequently, it is possible to increase the spatialresolution of the sample to be measured.

Also, because the pulsed light is deflected at the planar mirror, it ispossible, as well as increasing the optical path length, to make theapparatus configuration extremely compact.

Because the optical path length of the pulsed-light emitting unit andthe aspherical mirror can be increased, it is possible make the distancebetween the aspherical mirror and the sample large, while maintaining adesired focal area. Therefore, sufficient space can be ensured aroundthe sample, in other words, space for the sample-unit entrance and exitoptical systems and the sample holder, thus allowing the degree offreedom for the analysis procedure to be increased.

In the same way as the incident-side optical path described above, thedetection-side optical path between the detector and the sample-unitentrance and exit optical systems has a configuration in which a planarmirror is disposed between the aspherical mirror and the detector toincrease the optical path length; therefore, it is possible to reduce,as much as possible, the focal area of the beam focused by theaspherical mirror, and consequently, it is possible to increase thespatial resolution of the sample to be measured.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] Outline configuration diagram of a conventional time-domainpulsed spectroscopy apparatus.

[FIG. 2] Outline configuration diagram of one embodiment of atime-domain pulsed spectroscopy apparatus of the present invention.

[FIG. 3] (a) Outline configuration diagram of an embodiment of anoptical-path-difference compensation mechanism for wave form signalacquisition in the time-domain pulsed spectroscopy apparatus of thepresent invention. (b) Diagram showing a configuration in whichconfigurations shown in (a) are disposed in parallel.

[FIG. 4] Outline configuration diagram of another embodiment of anoptical-path-difference compensation mechanism for wave form signalacquisition in the time-domain pulsed spectroscopy apparatus of thepresent invention.

[FIG. 5] (a) Outline configuration diagram of another embodiment of anoptical-path-difference compensation mechanism for wave form signalacquisition in the time-domain pulsed spectroscopy apparatus of thepresent invention. (b) Magnified view of part of (a).

[FIG. 6] Outline configuration diagram of another embodiment of anoptical-path-difference compensation mechanism for wave form signalacquisition in the time-domain pulsed spectroscopy apparatus of thepresent invention.

[FIG. 7] (a) Outline configuration diagram of another embodiment of anoptical-path-difference compensation mechanism for wave form signalacquisition in the time-domain pulsed spectroscopy apparatus of thepresent invention. (b) Diagram showing a case where gate members and areflector in (a) are moved.

REFERENCE NUMERALS

-   -   1 pulsed laser light source    -   2 splitting unit    -   8 sample    -   12 detector    -   20 time-domain pulsed spectroscopy apparatus    -   26, 27, 28, 29 aspherical mirror    -   30 auxiliary optical unit    -   31 sample holder unit    -   32, 33, 34 sample-unit entrance optical system    -   35, 36, 37 sample-unit exit optical system    -   41, 42 optical-path-length varying unit or optical delay unit    -   51, 52, 53 reflector    -   61, 62, 63, 64 reflector    -   71, 73, 75 gate member    -   81, 82, 83 reflector    -   91, 93 gate member    -   101, 102 reflector    -   112 gate member    -   115 reflector

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 2 shows the outline configuration of an embodiment of a time-domainpulsed spectroscopy apparatus and an optical-path-differencecompensation device for wave form signal acquisition. The sameconstituent elements as those in FIG. 1 are assigned the same referencenumerals and a description thereof is omitted.

This time-domain pulsed spectroscopy apparatus 20 includes a pulsedlaser light source 1. Pulsed laser light L1 from this pulsed laser lightsource 1 is guided to a splitting unit 2 that splits it into excitationpulsed laser light L2 and detection pulsed laser light L3.

The time-domain pulsed spectroscopy apparatus 20 further includes apulsed-light emitting unit 5 that emits pulsed light includingwavelengths in the far-infrared wavelength region upon being irradiatedwith the excitation pulsed laser L2 and a detector 12 for detecting awave form signal of the electric field intensity of reflected pulsedlight from a sample 8, which is irradiated with the pulsed light fromthis pulsed-light emitting unit 5.

Between the pulsed-light emitting unit 5 and the detector 12 areprovided a sample holder 31 for holding the sample 8; a sample-unitentrance optical system 32, 33, and 34 for conveying pulsed light fromthe pulsed-light emitting unit to the sample; and a sample-unit exitoptical system 35, 36, and 37 for conveying pulsed light reflected fromthe sample due to this irradiation towards the detector 12.

Furthermore, the time-domain pulsed spectroscopy apparatus 20 includesat least one optical-path-length varying unit (a corner cube mirror inthe case of FIG. 2) 41 for setting a photometric range and at least oneoptical delay unit 42 (a corner cube mirror in the case of FIG. 2) forwave form signal measurement. Here, the optical-path-length varying unit41 is a movable reflector that can be scanned.

Driving devices (not shown in the drawing) for automatic scanning areprovided in the optical-path-length varying unit 41 for setting thephotometric range and in the optical delay unit 42 for wave form signalacquisition, and in addition, a computer control apparatus (not shown inthe drawing) for automatically controlling these driving devices isprovided. (However, regarding the reflectors 41 and 42, it is alsoacceptable that the former is used for wave form signal measurement andthe latter is used for setting the photometric range.)

Furthermore, the sample holder 31 and the sample-unit entrance and exitoptical systems 32, 33, 34, 35, 36, and 37 are provided inside anauxiliary optical unit 30, which can be detached from the time-domainpulsed spectroscopy apparatus and replaced.

An ellipsoidal mirror (aspherical mirror) 26 and a planar mirror 27,serving as optical elements, are provided in the incident-side opticalpath between the pulsed-light emitting unit 5 and the auxiliary opticalunit 30. The ellipsoidal mirror 26 converges the pulsed light from thepulsed-light emitting unit 5. The planar mirror 27 is located betweenthe pulsed-light emitting unit 5 and the ellipsoidal mirror 26 andserves to deflect the pulsed light from the pulsed-light emitting unit5. There may be one ellipsoidal mirror 26 and one planar mirror 27, asin the present embodiment, or a plurality thereof may be combined.

An ellipsoidal mirror (aspherical mirror) 28 and a planar mirror 29,serving as optical elements, are provided in the detection-side opticalpath between the detector 12 and the auxiliary optical unit 30. Theellipsoidal mirror 28 converges the reflected pulsed light from thesample 8. The planar mirror 29 is located between the ellipsoidal mirror28 and the detector 12 and serves to deflect the reflected pulsed lightfrom the ellipsoidal mirror 28. There may be one ellipsoidal mirror 28and one planar mirror 29, as in the present embodiment, or a pluralitythereof may be combined.

The ellipsoidal mirror 26, the planar mirror 27, the ellipsoidal mirror28, the planar mirror 29, which are optical elements, and otherunillustrated optical systems have an optical design such that they areoptically aligned with respect to this auxiliary optical unit 30.

This embodiment is configured to detect a wave form signal of theelectric field intensity of the reflected pulsed light from the sample.Of course, it may be configured to detect a wave form signal of theelectric field intensity of transmitted pulsed light.

In the time-domain pulsed spectroscopy apparatus of the presentinvention, configured as described above in outline, preparations forsample measurement are carried out as follows.

First, the sample 8 to be measured is attached to the sample holder 31in the auxiliary optical unit 30. Then, the auxiliary optical unit 30 isloaded in the time-domain pulsed spectroscopy apparatus 20. Then, inorder to set an origin for the time-series position of an output signalfor a specific optical path length in the sample-unit entrance and exitoptical systems 32, 33, 34, 35, 36, and 37 inside this auxiliary opticalunit 30, the driving device and computer control apparatus, which arenot shown, are operated to scan the reflector 41 for setting thephotometric range. Thus, preparations for sample measurement arecompleted.

The time-domain pulsed spectroscopy apparatus of the present inventionalso carries out sample measurement in substantially the same way as theconventional apparatus shown in FIG. 1.

More specifically, the pulsed laser light L1 emitted from the lightsource 1 is divided, by the splitting unit 2, into the excitation pulsedlaser light (pump pulsed light) L2 and the detection pulsed laser light(sampling pulsed light) L3.

The excitation pulsed laser light L2 is radiated onto the pulsed-lightemitting unit 5 via a lens 4. Due to this irradiation, the pulsed-lightemitting unit 5 emits a far-infrared electromagnetic pulse. After thisfar-infrared electromagnetic pulse has its optical path deflected by theplane mirror 27, it is guided to the ellipsoidal mirror 26 where it isfocused. The far-infrared electromagnetic pulse guided inside theauxiliary optical unit 30 is focused via the sample-unit entranceoptical system 32, 33, and 34 and is radiated onto the sample 8. Thereflected pulsed electromagnetic wave reflected from the sample 8,including optical information about the sample 8, is reflected, via thesample-unit entrance optical system 35, 36, and 37, at the ellipsoidalmirror 28 outside the auxiliary optical unit 30, and is thereafterdeflected at the plane mirror 29 and then guided to the detector 12.

On the other hand, the detection pulsed laser light L3 split off at thesplitting unit 2 defines the conductivity of the detector 12 only atthat instant and enables detection, as an electrical current, of theelectric field intensity of the reflected pulsed electromagnetic wavearriving from the sample 8 at that instant. Here, by applying a delaytime difference at predetermined time intervals to the detection pulsedlaser light L3 with respect to the excitation pulsed laser light L2, itis possible to acquire a wave form signal of the electric fieldintensity of the reflected pulsed electromagnetic wave from the sample8.

Although it is not illustrated in the drawings, this time-domain pulsedspectroscopy apparatus may be provided with a reflector exclusively foradjusting the temporal origin.

Therefore, according to the present embodiment, the pulsed light emittedfrom the pulsed-light emitting unit 5 is deflected by the plane mirror27 disposed between the pulsed-light emitting unit 5 and the ellipsoidalmirror 26. Thus, it is possible to increase the optical path length ofthe pulsed-light emitting unit 5 and the ellipsoidal mirror 26 and thefocal area of the beam focused by the ellipsoidal mirror 26 can bereduced as much as possible; consequently, the spatial resolution of thesample 8 to be measured can be improved.

Also, since the pulsed light is deflected by the plane mirror 27, aswell as increasing the optical path length, it is also possible to makethe apparatus configuration extremely compact.

Furthermore, because the optical path length of the pulsed-lightemitting unit 5 and the ellipsoidal mirror 26 can be increased, it ispossible to increase the distance between the ellipsoidal mirror 26 andthe sample 8 while maintaining the desired focal area. Accordingly,sufficient space can be secured for installing the auxiliary opticalunit 30, thus facilitating analysis.

Similarly to the incident-side optical path, the detection-side opticalpath between the detector 12 and the auxiliary optical unit 30 isconfigured such that the planar mirror 29 is disposed between theellipsoidal mirror 28 and the detector 12 to increase the optical pathlength; therefore, the focal area of the light beam converged by theellipsoidal mirror 28 can be reduced as much as possible, andconsequently, it is possible to improve the spatial resolution of thesample 8 to be measured. Furthermore, similarly to the incident-sideoptical path, the apparatus configuration can be made compact, and asufficient space for installing the auxiliary optical unit 30 can beensured.

FIG. 3(a) shows the outline configuration of another embodiment of anoptical-path-difference compensation mechanism for wave form signalacquisition of the time-domain pulsed spectroscopy apparatus of thepresent invention.

In this embodiment, in the incident-side optical path from the splittingunit to the pulsed-light emitting unit and/or in the detection-sideoptical path from the splitting unit to the detector, a plurality ofoptical-path-length varying units and/or optical delay units (reflectorsin the case of FIG. 3) are disposed opposite each other such that thepaths of light incident on and reflected from the reflectors areparallel and the optical paths are staggered. In the case shown in thefigure, the reflectors are corner cube mirrors. In this configuration,the pulsed laser light L2 or L3 incident on the scanning mechanism aresequentially reflected at corner cube mirrors 51, 52, 53, . . . , guidedoutside the scanning mechanism, and sent to the pulsed-light emittingunit 5 or the detector 12.

Due to this configuration, compared to the case of a single reflector,the optical path length can be varied by amounts according to the numberof reflectors. Also, according to this configuration, it is possible togreatly vary the optical path length in a case where there isinsufficient space in the scanning direction of the reflector but wherethere is sufficient space in a direction orthogonal to the scanningdirection. In this embodiment, as shown in FIG. 3(b), scanningmechanisms with a configuration like that in FIG. 3(a) may be disposedin parallel in the incident-side optical path and/or the detection-sideoptical path.

As shown in FIG. 3(b), optical-path-length varying units and/or opticaldelay units with a configuration like that in FIG. 3(a) may be disposedin parallel in the incident-side optical path and/or the detection-sideoptical path.

FIG. 4 shows the outline configuration of another embodiment of anoptical-path-difference compensation mechanism for wave form signalacquisition in the time-domain pulsed spectroscopy apparatus of thepresent invention.

This embodiment is configured such that two reflectors for setting thephotometric range (corner cube mirrors in the figure) and two reflectorsfor wave form signal measurement (corner cube mirrors in the figure) (61and 62, and 63 and 64) are aligned and scanned simultaneously, and thereflectors 61 and 62 for setting the photometric range and thereflectors 63 and 64 for wave form signal measurement are disposedopposite each other such that the optical paths are staggered. In thisconfiguration, the excitation pulsed light L2 or the detection pulsedlight L3, split into two by the splitting unit, is reflected by themirror 65; thereafter, it enters the scanning mechanism, is reflected inturn at the reflectors 63, 61, 64, and 62 for setting the photometricrange and for wave form signal measurement, is guided outside thescanning mechanism, and is then reflected at the mirrors 66 and 67 andsent to the pulsed-light emitting unit 5 and the detector 12.

This configuration, compared to the case of a single corner cube mirror,has the feature that the optical path length can be changed by a factorof two relative to the scanning of the reflector. Therefore, anadvantage is provided in that photometric range setting and setting forwave form signal measurement can be performed quickly. The configurationin FIG. 4 may be used in either the optical-path-length varying unit orthe optical delay unit.

FIG. 5(a) shows an outline configuration of another embodiment of anoptical-path-difference compensation mechanism for acquiring a wave formsignal in the time-domain pulsed spectroscopy apparatus of the presentinvention.

In the embodiment in FIG. 5(a), optical-path-length varying units 81,82, 83, . . . for setting the measurement range are movable or fixedreflectors, and by providing any of these reflectors with gate members71, 73, and 75 for passing or blocking pulsed light to these reflectors,at least at the incident side of the pulsed light to these reflectors,and switching between these passing or blocking modes, it is possible toadd optical paths via one, two, or more of the reflectors 81, 82, 83, .. . to extend the optical path length, and/or it is possible to skipone, two, or more of the reflectors 81, 82, 83, . . . to shorten theoptical path length. Also, in the case shown in FIG. 5, the gate membersare reflecting mirrors, and reflecting mirrors 72, 74, . . . forreflecting the pulsed light reflected from the reflectors 81, 82, 83, .. . towards the adjacent reflectors are provided. In this embodiment,the passage or blocking of at least one reflecting mirror (gate member)is carried out by inserting it into and removing it from the opticalpath of the reflecting mirror by rotation of the reflecting mirror. Inthe figure, the arrows in the vicinity of the reflecting mirrors and thesolid lines and dotted lines indicating the reflecting mirrorsschematically illustrate switching between the passing and blockingstates of the reflecting mirrors.

The operation of this embodiment will be described using FIG. 5(b),which is an enlarged view of part of FIG. 5(a). For example, beforeswitching, when the reflecting mirror 71 is inserted into the opticalpath (solid line) and the reflecting mirror 72 (solid line) is removedfrom the optical path, the laser light L4 is reflected at the reflectingmirror 71, becomes L41, and proceeds as L5. In such a case, thereflector 81 is skipped. In contrast, when the reflecting mirrors 71 and72 are switched and the reflecting mirror 71 is removed from the opticalpath and the reflecting mirror 72 is inserted into the optical path, asshown by the dotted lines, the laser light L4 is reflected, as L42, atthe reflector 81, becomes L43, is reflected again, becomes L44, isreflected at the reflecting mirror 72, and proceeds as L5. By switchingin this way, an optical path length via the reflector 81 is added.Accordingly, if this switching order is reversed, conversely, theoptical path via the reflector 81 is eliminated, and the optical pathlength is reduced. The configuration in FIG. 5 may be used in either theoptical-path-length varying unit or the optical delay unit.

FIG. 6 shows the outline configuration of another embodiment of anoptical-path-difference compensation mechanism for acquiring a wave formsignal in the time-domain pulsed spectroscopy apparatus of the presentinvention.

This embodiment has a configuration in which a plurality of reflectors101, 102, . . . are disposed in appropriate positions according to theapplication, and the optical path length is varied by gate members 91,93, . . . and reflecting mirrors 92, 94, . . . for sending light to theadjacent reflectors. In the case shown in FIG. 6, the gate members arereflecting mirrors.

In this embodiment, when the gate members 91, 93, . . . and thereflecting mirror 92, 94, . . . for sending light to the adjacentreflectors are disposed at the solid-line positions, the pulsed lightincident on the optical-path-length varying unit is first reflected atthe gate member 91, passes near the reflecting mirror 92, the gatemember 93, and the reflecting mirror 94, and is reflected at thereflecting mirror 95 to be guided outside. In this case, measurement ofthe sample is not carried out using the reflectors 101 and 102. On theother hand, by switching the gate member 91 and the reflecting mirror 92to the dotted-line positions, it is possible, with the pulsed light, tomeasure the sample using the reflector 101 (reflection measurement inthe figure). Furthermore, by switching the gate member 91 and thereflecting mirror 92 to the solid-line positions and switching the gatemember 93 and the reflecting mirror 94 to the dotted-line positions, itis possible to measure the sample using the reflector 102 (gas-cellmeasurement in the figure).

FIG. 7(a) and FIG. 7(b) show the outline configuration of anotherembodiment of an optical-path-difference compensation mechanism foracquiring a wave form signal in the time-domain pulsed spectroscopyapparatus.

In this embodiment, passing or blocking of at least one gate member 112is performed by inserting it into and removing it from the optical pathby translating the gate member 112. In particular, in the case shown inFIG. 7, the gate member 112 and a reflector 115 are provided together ona motion apparatus 116. Furthermore, a reflecting mirror 113 forreflecting and forwarding pulsed light reflected from the reflector 115towards a reflecting mirror 114 is provided on the motion apparatus 116.In the case shown in the figure, the gate member 112 is a reflectingmirror.

In this case, when the motion apparatus is disposed at the position inFIG. 7(a), the pulsed light reflected from the reflecting mirror 111passes near the gate member 112 and the reflecting mirror 113 and isreflected at the reflecting mirror 114 to be guided outside. When themotion apparatus 116 is moved from the position in FIG. 7(a) to theposition in FIG. 7(b), the gate member 112, the reflecting mirror 113,and the reflector 115 are translated together, thus adding the opticalpath via the reflector 115 to extend the optical path length, whichenables measurement using the reflector 115.

1. A time-domain pulsed spectroscopy apparatus comprising: a pulsedlaser light source; a splitting unit configured to split pulsed laserlight from the pulsed laser light source into excitation pulsed laserlight and detection pulsed laser light; a pulsed-light emitting unitconfigured to emit pulsed light including wavelengths in thefar-infrared wavelength region due to irradiation of the excitationpulsed laser; a detector configured to detect a wave form signal of theelectric field intensity of reflected or transmitted pulsed light fromthe sample onto which the pulsed light from the pulsed-light emittingunit is radiated; a sample holder configured to hold the sample; andsample-unit entrance and exit optical systems configured to guide thepulsed light from the pulsed-light emitting unit to the sample and toguide to the detector pulsed light reflected from or transmitted throughthe sample due to the irradiation, wherein the time-domain pulsedspectroscopy apparatus further comprises: at least oneoptical-path-length varying unit for setting a photometric range,disposed in an incident-side optical path from the splitting unit to thepulsed-light emitting unit and/or in a detection-side optical path fromthe splitting unit to the detector; and at least one optical delay unitfor the wave form signal measurement, disposed in the incident-sideoptical path from the splitting unit to the pulsed-light emitting unitand/or in the detection-side optical path from the splitting unit to thedetector.
 2. A time-domain pulsed spectroscopy apparatus according toclaim 1, wherein the optical-path-length varying unit for setting aphotometric range is a movable reflector.
 3. A time-domain pulsedspectroscopy apparatus according to claim 1, wherein: theoptical-path-length varying unit for setting a photometric range is amovable or fixed reflector; and either reflector includes, at theincident side of the pulsed light to the reflector, a gate memberconfigured to pass or block the pulsed light to the reflector, and byswitching between passing or blocking, it is possible to add an opticalpath via one, two, or more of the reflectors to extend the optical pathlength and/or to skip one, two, or more of the reflectors to shorten theoptical path length.
 4. A time-domain pulsed spectroscopy apparatusaccording to claim 3, wherein passing or blocking of at least one of thegate members is performed by inserting and removing the gate member, bytranslational motion, into and from the optical path.
 5. A time-domainpulsed spectroscopy apparatus according to claim 3, wherein passing orblocking of at least one of the gate members is performed by insertingand removing the gate member, by rotation, into and from the opticalpath.
 6. A time-domain pulsed spectroscopy apparatus according to one ofclaims 1 to 5, further comprising: a driving device configured toautomatically scan the optical-path-length varying unit and/or theoptical delay unit; and a computer control apparatus configured toautomatically control the driving device.
 7. A time-domain pulsedspectroscopy apparatus according to claim 1, wherein the sample holderand the sample-unit entrance and exit optical systems are providedinside an auxiliary optical unit that can be attached to and removedfrom the time-domain pulsed spectroscopy apparatus to enable replacementthereof.
 8. A time-domain pulsed spectroscopy apparatus according toclaim 7 having an optical design that provides optical alignment withrespect to the auxiliary optical unit.
 9. A time-domain pulsedspectroscopy apparatus comprising: a pulsed laser light source; asplitting unit configured to split pulsed laser light from the pulsedlaser light source into excitation pulsed laser light and detectionpulsed laser light; a pulsed-light emitting unit configured to emitpulsed light including wavelengths in the far-infrared wavelength regiondue to irradiation of the excitation pulsed laser; a detector configuredto detect a time-serial signal of the electric field intensity ofreflected or transmitted pulsed light from the sample onto which thepulsed light from the pulsed-light emitting unit is radiated; a sampleholder configured to hold the sample; and sample-unit entrance and exitoptical systems configured to guide the pulsed light from thepulsed-light emitting unit to the sample and to guide to the detectorpulsed light reflected from or transmitted through the sample due to theirradiation, wherein, from the pulsed-light emitting unit to thesample-unit entrance and exit optical systems and/or from the detectorto the sample-unit entrance and exit optical systems, one or a pluralityof planar mirrors and one or a plurality of aspherical mirrors aredisposed in this order.
 10. A time-domain pulsed spectroscopy apparatusaccording to claim 1 wherein, in the time-domain pulsed spectroscopyapparatus comprising: a pulsed laser light source; a splitting unitconfigured to split pulsed laser light from the pulsed laser lightsource into excitation pulsed laser light and detection pulsed laserlight; a pulsed-light emitting unit configured to emit pulsed lightincluding wavelengths in the far-infrared wavelength region due toirradiation of the excitation pulsed laser; a detector configured todetect a wave form signal of the electric field intensity of reflectedor transmitted pulsed light from the sample onto which the pulsed lightfrom the pulsed-light emitting unit is radiated; a sample holderconfigured to hold the sample; and sample-unit entrance and exit opticalsystems configured to guide the pulsed light from the pulsed-lightemitting unit to the sample and to guide to the detector pulsed lightreflected from or transmitted through the sample due to the irradiation,from the pulsed-light emitting unit to the sample-unit entrance and exitoptical systems and/or from the detector to the sample-unit entrance andexit optical systems, one or a plurality of planar mirrors and one or aplurality of aspherical mirrors are disposed in this order.